The term decorative panel in the sense of the invention means wall, ceiling or floor panels comprising a decor applied to a carrier plate. Decorative panels are used in various ways in the field of interior construction of rooms as well as for the decorative cladding of structures, for example in exhibition stand constructions. One of the most common areas of application of decorative panels is their usage as a floor paving. Herein, the decorative panels often have a decor which should simulate a natural material.
Examples of such simulated natural materials are wood species such as maple, oak, birch, cherry wood, ash, walnut, chestnut, wenge or exotic wood such as Panga-Panga, mahogany, bamboo and Bubinga. Moreover, natural materials, such as stone surfaces or ceramic surfaces, are often simulated.
Hitherto such decorative panels are often manufactured as laminates in which a decorative paper preprinted with a desired decor is applied on a carrier plate and a so-called overlay, in turn, is applied onto the decorative layer. After a counteracting paper has been applied on the side of the carrier plate opposing the decorative paper, if desired, the layered structure obtained is firmly bonded together by means of appropriate pressure and/or heat-activated adhesives.
Dependent on the desired areas of application of the decorative panels they could be produced from different materials. Herein, in particular the material of the carrier can be selected in dependence of the area of application. Thus, the carrier, for example, can consist of a wood-based material, inasmuch as the decorative panel is not exposed to excessive moisture or weather conditions. If the panel, for example, is to be used in wet rooms or in the outdoor area, the carrier, for example, can consist of a plastic material.
Herein, wood-based materials in the sense of the invention in addition to solid wood-based materials comprise materials such as plywood board, composite lumber, blockboard, veneer plywood, laminated veneer lumber, parallel strand lumber and bending plywood. In addition wood-based materials in the sense of the invention are understood to include chipboards such as pressboards, extruded boards, oriented structural boards (OSB) and laminated strand lumber as well as wood fibre materials such as wood fibre insulation boards (HFD), hard and medium-hard fibreboards (MB, HFH) and particularly medium-density fibreboards (MDF) and high-density fibreboards (HDF). Moreover, modern wood-based materials such as wood-polymer materials (wood plastic composite, WPC), sandwich boards made of a lightweight core material such as foam, hard foam or paper honeycombs and a wood layer applied thereon as well as chipboards minerally hardened, for example with cement, are wood-based materials in the sense of the invention. Moreover, cork represents a wood-based material in the sense of the invention.
Plastic materials which can be used in the production of corresponding panels are, for example, thermoplastics such as polyvinyl chloride, polyolefines (such as polyethylene (PE), polypropylene (PP)), polyamides (PA), polyurethanes (PU), polystyrene (PS), acrylonitril butadiene styrene (ABS), polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate (PET), polyether ether ketone (PEEK) or mixtures or copolymerizates thereof. The plastic materials can include common fillers, such as calcium carbonate (chalk), aluminum oxide, silicagel, quartz powder, wood flour, gypsum. In addition they can be coloured in a known way.
In the sense of the invention the term “direct printing” means applying a decor directly onto the carrier of a panel or onto an unprinted fibre material layer applied to the carrier. In contrast to conventional methods in which a decorative layer previously printed with a desired decor is applied onto the carrier in direct printing the decor is printed directly in the course of the panel production. Herein, different printing techniques can be used such as flexographic printing, offset printing or silk-screen printing. Herein, in particular digital printing techniques can be used such as inkjet methods and laser printing methods.
In the sense of the invention the term fibre materials means materials such as paper and non-woven fabrics on the basis of plant, animal, mineral or even synthetic fibres as well as cardboards. Examples of fibre materials on the basis of plant fibres in addition to papers and non-woven fabrics made of cellulose fibres are biomass such as straw, maize straw, bamboo, leaves, algae extracts, hemp, cotton or oil palm fibres. Examples of animal fibres are keratin-based materials such as wool or horsehair. Examples of mineral fibre materials are mineral wool or glass wool.
For protecting the applied decorative layer normally a wearing or top layer is applied on top of the decorative layer. A wearing and/or top layer in the sense of the invention is a layer applied as an outer finish which particularly protects the decorative layer against wear or damage by dirt, influence of moisture or mechanical impacts such as abrasion. Herein it can be provided that the wearing layer includes hard materials such as titan nitride, titan carbide, silicon nitride, silicon carbide, boron carbide, tungsten carbide, tantalum carbide, aluminum oxide (corundum), zircon oxide or mixtures thereof, in order to increase the wear resistance. Herein, it can be provided that the hard material is included in an amount between 5% by weight and 40% by weight, preferably between 15% by weight and 25% by weight, in the composition of the wearing layer. The hard material preferably has an average core diameter between 10 μm and 250 μm, more preferably between 10 μm and 100 μm. In this way it is achieved in a preferred way that the composition of the wearing layer forms a stable dispersion and a decomposition or precipitation of the hard material within the composition of the wearing layer can be avoided. For the formation of a corresponding wearing layer according to one embodiment of the invention it is provided that the composition including hard material and adapted to be cured by radiation is applied with a concentration between 10 g/m2 and 250 g/m2, preferably between 25 g/m2 and 100 g/m2. The application can be implemented, for example, by rollers, such as rubber rollers, or by means of pouring devices. According to a further embodiment of the invention it can be provided that the hard material at the time of application of the composition of the wearing layer is not included within the composition, but is spread in the form of particles onto the applied composition of the wearing layer and subsequently is cured.
In many cases it is provided that a surface texture matching with the decor is included in such wearing or top layers. A surface texture matching with the decor means that the surface of the decorative panel comprises a haptic structure which according to its shape and pattern corresponds to the applied decor such as to achieve a reproduction of a natural material as close to the original as possible even with respect to the haptic. Herein, it can be provided that the carrier plate already comprises a texture and an alignment of a printing tool for applying the decor with respect to the carrier plate is implemented by means of the texture of the carrier plate which is detected by optical methods. Herein, for aligning the printing tool and the carrier plate relative to each other a relative movement between the printing tool and the carrier plate necessary for the alignment is implemented by shifting the carrier plate or by shifting the printing tool. According to a further embodiment of the invention it is provided that a texturing of the decorative panel is implemented subsequently to the application of the top and/or wearing layer. To this end it can be preferred to apply as the top and/or wearing layer a curable composition and a curing process is done only to an extent that only a partial curing of the top and/or wearing layer is achieved. In the thus partially cured layer by means of appropriate tools, such as a hard metal texture roller or a die, a desired surface texture is embossed. Herein, the embossing process is implemented corresponding to the applied decor. In order to ensure a sufficient matching of the texture to be produced with the decor it may be provided that the carrier plate and the embossing tool are to be aligned to each other by corresponding relative movements. Subsequently to the production of the desired texture within the partially cured top and/or wearing layer a further curing step is implemented with respect to the now textured top and/or wearing layer.
One problem that may occur during direct printing of decorative panels is that a deterioration of the print image occurs in the course of the production process. Dependent on the selected printing method a visible blurring of the print image can occur during the production process. If, for example, an inkjet method is used for applying the decor, after a certain production time period a clearly recognizable blurring occurs in the decor print image which is not attributable to possible contaminations of the printhead or a change of the ink.